Biden himself fueled much of the talk, thanks to his appearance at an inaugural party for Iowans - who will open the 2016 contest with caucuses - to his animated handshaking during Monday's parade on Pennsylvania Avenue.

One factor in Biden's decision: Will soon-to-depart Secretary of State Hillary Rodham Clinton also seek the presidency in three years?

"Look, I haven't made that judgment, and Hillary hasn't made that judgment," Biden said on CNN. "But I can tell you what, everything that should be done over the next two years that I should be part of what would have to be done whether I run or I don't run."

Again, he noted: " If this administration is successful, whoever is running as a Democrat is better position to win. If we are not successful, whoever runs as a nominee is going to be less likely to win."